Browsing by Author "Hoffmann, Timm"

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    Aloe Pillansii on Cornell's Kop : are population changes a result of intrinsic life history patterns or climate change?
    (2004) Duncan, John A; Hoffmann, Timm
    Aloe pillansii populations in the biodiversity hotspot of the Succulent Karoo in Southern Africa are thought to be under threat of extinction. This study investigated the population at the type locality; Cornell's Kop in the Richtersveld, South Africa. It has been suggested that theft, animal damage and more recently climate change have caused a decline in the population by over 50% in the last decade, however very little is known about this rare species. Repeat photography and surveys were used to analyse life history patterns and dynamics of the population and thus establish what the potential threats to this keystone species actually are. Repeat photography indicates that there have been high rates of adult mortality over the last fifty years (1.8% of the population dies annually), which results in an average predicted lifespan of 39 years for the remaining adult population on Cornell's Kop. However, a recent survey reported that over 40% of the population recorded were seedlings, which weren't found in a 1995 survey, which is indicative of a recent recruitment pulse on Cornell's Kop and that conditions on the hill are still habitable for A. pillansii. Growth analyses suggest that A. pillansii has an average annual growth rate of 20 mm.yr⁻¹, which in tum means that 8 m individuals may be up to 453 years old. This long-lived strategy would require A. pillansii to only recruit infrequently, during periods of high rainfall, in order to sustain a viable population, which is consistent with findings on other large desert succulents. Seedling ages were estimated from their heights and it was found that 50% of the seedlings appear to have germinated five to ten years ago; this is consistent with rainfall records from the area which indicate that rainfall was consistently above the annual average for this same period. The findings indicate that although the adult A. pillansii population is declining, the presence of 30 seedlings suggest that the population is entering a recruitment phase after just coming out of a lengthy senescent phase. Although A. pillansii 's extensive lifespan makes it a potentially useful indicator species of climate change, the evidence presented in this study does not suggest that climate change has affected the dynamics of this population.
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    An analysis of vegetation pattern and its relationship to NDVI data in the Namaqualand area, South Africa
    (2003) Fox, Sarah-Jane Caroline; Hoffmann, Timm; Hoare, David
    The Namaqualand area in the North Western Cape, South Africa is unique in comparison to other similar semi-arid areas of the world. It has a high biodiversity and endemism and is consequently an area of interest for a growing number of conservation initiatives. Climate plays an important role in influencing the phenology and growth of the vegetation in the area. Remote sensing techniques were used to reveal the vegetation patterns in the greater Namaqualand area and to relate them to climatic variables. To do this we used the normalised difference vegetation index (NDVI) to relate biomass to altitude, rainfall and vegetation type. Each vegetation type in the area had a unique temporal signature and the climatic variables influencing the summer rainfall and winter rainfall vegetation types differed significantly from each other. Mean annual NDVI was significantly correlated to precipitation and potential evapotranspiration (PET) (r = 0.60, -0.63 respectively). A multiple regression model explained 52% of the variance when Mean Annual NDVI was related to climatic variables. Mean NDVI in August (the month of maximum NDVI in most of Namaqualand) was significantly related to PET and the current plus two previous months of precipitation (r = -0.72 and 0.74 respectively). A multiple regression model for mean NDVI in August and climatic variables explained almost 58% of the variance. The results suggest that NDVI can be used successfully as a measure of growth and phenology in the Namaqualand area and that NDVI could be used in climate models, drought prediction, desertification predictions and a number of other applications in the future.
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    Changing land use / land cover around an urban estuary : implications for ecosystem functioning
    (2006) Jack, Sam; Hoffmann, Timm
    The changing spatial and temporal patterns in land use/land cover surrounding Zandvlei estuary were investigated over the period 1944 to 2005. Changes in the extent of four terrestrial and two aquatic land use/land cover categories were mapped from high quality aerial photographs using ArcView GIS. Basic spatial analyses were performed to quantify changes in area, 'edge-effects' and relative dominance through time. Semi-natural and seasonally inundated classes accounted for over 70% of land cover in 1944, but declined steadily as urban land use and permanently inundated land cover expanded to a present-day extent of 42% and 19% respectively. The following major drivers of change were identified: 1) the construction of the railway embankment bisecting Westlake wetland and Zandvlei estuary, which led to sedimentation and a change in plant species composition of the wetland, but decreased nutrient inflows into the vlei; 2) agricultural practices within the catchment at the start of the 20th century which increased sediment and nutrient inflows; 3) elevated water levels due to dredging operations between 1947 and 1961, which resulted in a significant loss of seasonally inundated land cover with concomitant changes in species composition and nutrient dynamics; and 4) urban development surrounding the vlei (with particular reference to Marina da Gama), which has expanded at the expense of semi-natural areas and significantly increased effluent and litter inputs into the vlei. A socially and ecologically balanced management policy governing the entire catchment is required to mitigate future impacts.
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    Current status and impact (2004-2015) of indigenous ungulate herbivory on the vegetation of Sanbona Wildlife Reserve in the Little Karoo
    (2017) Vorster, Liesl; Todd, Simon W; Hoffmann, Timm
    Game farming is becoming more popular in southern Africa and the introduction of large indigenous ungulates into confined enclosed areas could alter plant communities and ecosystem processes. This is of particular concern in semi-arid rangelands of the Succulent Karoo where the evolutionary history of grazing is not clear and the compatibility of large herbivores in confined areas remains to be demonstrated. The establishment of Sanbona Wildlife Reserve, a 54 000 hectare private game reserve in the Little Karoo, which converted from livestock farming to game farming, allows an opportunity to study the vegetation dynamics in a confined plant-herbivore system. This study investigates the current community structure and the changes in the floral composition and vegetation structure of enclosed and comparable sites subjected to grazing by large herbivores after twelve years (2004-2015). It also determines the relative effect of grazing and rainfall on the observed patterns. Finally, the implications of these findings for management are discussed. Data from drop-point surveys in fenced (exclosure) and unfenced (grazed) plots in the dominant vegetation types as well as annual and seasonal rainfall totals, stocking rates of herbivores and annual game census information, were analysed. These were used in multivariate ordination techniques, regressions and linear mixed-effects models to determine the communities and their relationship with herbivory and rainfall over time and identify a set of indicator species. The annual game census information was used to determine areas of herbivore preference or 'hotspots' and for the identification of highly-utilised areas. Cluster analysis, using the flexible beta method in PC-Ord, was used to determine the current plant communities. Non-metric multidimensional scaling ordination (NMS) was used to determine the relationship of these communities with the environmental variables and illustrate the trajectories in floristic data. Species were also assigned to plant growth forms and examined as communities and growth form types. The Bray-Curtis distance measures were used to investigate the difference between each treatment over time, within each vegetation community and between treatments. Finally, the effects of rainfall and herbivory were examined using linear mixed-effects models of change over time vs the various potential determinants of change using lmer functions in R. Four communities were identified. These communities corresponded well with to the vegetation type descriptions for Western Little Karoo, Little Karoo Quartz Vygieveld and Renosterveld as described in the National Vegetation Map of Mucina and Rutherford (2006). However, the Western Little Karoo was too broad and two communities were recognised within this vegetation type. The finer scale mapping by Vlok et al. (2005) corresponded relatively well to these communities. Results showed an increase in species richness, abundance and cover over time, with the ungrazed plots experiencing more change than the plots exposed to grazing. Most growth forms exhibited an increase in cover, although low leaf succulents declined in both grazed and ungrazed plots. Medium evergreen shrubs declined in the exclosures and stem succulents declined in the grazed plots. The effects were found in both grazed and ungrazed treatments. In addition, many species which declined in abundance were unpalatable or toxic to herbivores. Because of this, the decline in cover of such species was not attributed to grazing, but was instead interpreted as being a response to other disturbance mechanisms, to competitive displacement and to rainfall events. The low stocking rates in the first five years of the study resulted in there being very little difference evident between the treatments. However, once stocking rates increased from 2008, both species richness and cover increased more rapidly in the ungrazed plots, compared to the grazed plots. An increase in palatable and unpalatable species was observed within both ungrazed and grazed plots indicating that grazing did not change the proportion of palatability classes. However, specific plots in the areas of high animal utilisation were more affected as indicated by the response of cover, species richness and palatable species in these specific plots. This suggests that the grazing pressure may be too high within those areas. The linear mixed-effect model supports the argument that grazing pressure is the dominant driver of the community change within grazed plots. Similarly, the results show that rainfall is the primary driver of the vegetation community in the absence of grazing. Timing, amount and intensity of rainfall can mask these impacts. Thus, the contribution of grazing to vegetation change can probably only be detected by tracking the trends over decades or longer. The use of indicators as a management tool is well documented. In order to identify indicators, a theoretical framework for determining indicators species in the different vegetation communities was created. This was based on the correlation between species abundance and sampling period in the different treatments, which identified species that have significantly increased or decreased over time as a result of the change in land use. Species identified as potential indicators were selected on the basis based on their abundance and ranged in lifespans and palatability. The indicators chosen need to be monitored into the future to confirm their utility as indicators. A small but significant difference between grazed and ungrazed plots suggest that herbivore impact is apparent. Identifying this trend indicates that the monitoring programme is providing a useful tool for assessing the impact of herbivores on an ongoing basis. The recovery process following the withdrawal of domestic livestock from Sanbona was much slower in the grazed plots than in the protected plots. Therefore, for the continued recovery of the vegetation to occur and for there to be a sustained increase in cover, active management of animal numbers needs to take place. The results from this study can contribute to future management decisions on the reserve and form a basis for future analyses.
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    The distribution and population structure of Aloe pillansii in South Africa, in relation to climate and elevation
    (2004) Bolus, Cosman; Hoffmann, Timm
    South Africa comprises almost 10% of known plant species and also has the only arid zone "hotspot" defined worldwide, namely the succulent Karoo. Anthropogenic climate change predictions for South Africa suggest rapid climate change in the next 50 years will have adverse effects on its vegetation biomes. This study shows how the aborescent succulent, Aloe pillansii, has a limited distribution due significantly to environmental and climatic variables and therefore it is potentially at risk given anthropogenic climate change predictions. The total South African A. pillansii population investigated is made up of 1202 individuals and is found in the Richtersveld, which is part of the Succulent Karoo. The A. pillansii individuals were sampled in terms of their height and geographical position and then defined into subpopulations by a distance of 2 kms of separation. The sub-populations were then evaluated in terms of their respective environmental and climatic variables acquired from a CCWR database for South Africa using Arc View 3.2. The sub-population size class distributions were also constructed so that population dynamics and recruitment could be investigated. The results show how the A. pillansii sub-populations are limited to a specific environmental and climatic range. The sub-populations group along similar environmental and climatic variables with the healthiest sub-populations found at lower elevation, higher temperatures and higher Potential Evapo-Transpiration. The climatic range of A. pillansii is also evident from the range of its environmental and climatic variables and the associated unhealthy sub-populations that lie on the extremes of this range. Recruitment was found to correlate strongly with the environmental and climatic variables, % winter rainfall and elevation, suggesting it is moisture limited. The evidence found in this study of A. pillansii 's specific environmental and climatic distribution may have negative implications for its future survival and conservation especially with present indications of anthropogenic climate change.
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    Effect of short term rest on riverine systems associated with heavy grazing in Paulshoek, Namaqualand, South Africa
    (2002) Monakisi, Charlotte; Allsopp, Nicky; Hoffmann, Timm
    Arid and semi-arid systems comprise one third of the earth's surfaces. The succulent karoo alone comprises approximately 1660 endemic species and is one of the world's hotspots in terms of diversity. Although these areas are of high ecological value less than 10% of arid systems are conserved. This study was conducted in Paulshoek a remote village in the Leliefontein area of the Namaqualand. Historically Paulshoek has been under continuous selective grazing since the 18th century. A fence line contrast is investigated in an area that was fenced three years ago and in one that has been exposed to heavy, continuous, selective grazing over the past century (both areas were fenced prior to fencing). The objective of this study was to investigate the effect of short-term rest on key vegetation demographic parameters as well as the physical characteristics of communal river systems. No significant differences in plant species richness were observed across the fence line. However, the numbers of plants of each species within the plots were significantly different, depending on presence or absence of grazing. The grazed sites had more species tolerant of grazing such as geophytes, annuals and toxic species such as Galenia africana. Heavy grazing in this ecosystem has resulted in increased proportions of unpalatable species with a slow reduction in the number of palatable species. Species cover was significantly reduced on the grazed sites; however, these reductions were insignificant for Lyceum cinereum species due to large standard deviations. Heavy grazing of palatable sedge species (Scirpus nodosus) resulted in significant reductions in the number of flowers of plants, in the grazed sites. Grazing not only reduced the size of the plants, it also reduced flowering, fruit set and recruitment rate. There was no significant difference in the physical and geomorphologic characteristics of the river across the fence-line. This study indicates that short-term rest has major implications for plant recovery. Educating communal farmers to use a farming system that insures temporary rest on certain areas of the rangelands at certain times of the year will go a long way in improving species richness in Namaqualand.
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    The effects of leaf harvesting on the morphology, reproduction and sap production of the Cape Aloe (Aloe Ferox)
    (2004) Greengrass, Catherine; Chadwick, Peter J; Hoffmann, Timm
    Harvesting of Aloeferox was estimated (in 1996) to bring in an annual income ofR4 million per year to rural communities alone - a vital source of income for full-time tappers who rely solely on Aloe ferox as their only form of financial survival. They are joined on occasion by casual-tappers who rely on tapping to supplement their incomes in times of hardship (Newton and Vaughan 1996). Landowner's also benefit by allowing harvesting on their land in exchange for a percentage of the harvest (Newton and Vaughan 1996). Trade in bitters sap or gel far outweighs that of other plant parts so care is taken by harvesters to keep the plants alive for future tapping. Leaves from only the lower third of the leaf rosette ( 10 - 15 leaves) are harvested, and 2 - 4 cm at the base of the leaves are left to prevent damage to vascular tissues (Newton and Vaughan 1996, Mac Farlane 2004). Populations are only harvested every 18 - 36 months allowing plants to recover from the loss of leaf material. Plants suffering from insect-infestation or disease are not harvested to avoid weakening the plant further and possibly causing death (Newton and Vaughan 1996). Effort is also made by landowners to relocate plants growing in areas they plan to transform and to monitor harvesting activities on their properties (Newton and Vaughan 1996). The vested interest in keeping the plants alive has inadvertently assured the preservation of populations at past harvesting levels although no formal conservation or resource management policy presently exists for A. ferox (Newton and Vaughan 1996). Effects of harvesting, which are not limited to the direct effect of leaf removal on the plant but include indirect effects - such as reduced reproductive output, reduced sap production and even trampling of recruits - have nonetheless raised concern for the long-term survival of populations (Newton and Vaughan 1996). This study addressed some of the indirect effects of harvesting on Aloe ferox on both population and individual plants levels. On the population level plant density, mortality, susceptibility to disease and sizeclass structure was compared between unharvested and harvested populations. On the individual plant level vegetative traits, flower production and sap production were compared between unharvested and harvested plants. One of few other studies on ecology of A. ferox by Hoffman (1988) assessed some of these characteristics for a population in Port Elizabeth, South Africa.
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    Habitat use, feeding ecology and the impact of re-introduced elephants (Loxodonta africana) on trees within a restricted conservation area in the semi-arid, Little Karoo, South Africa
    (2009) Erasmus, Krynauw; Hoffmann, Timm
    The reintroduction of free-roaming elephants on the 540 km2 Sanbona Wildlife Reserve in the Little Karoo, Western Cape, South Africa, raised concerns over the possible negative impacts that these animals may have on the biodiversity of the property, especially the tree component. The main objectives of this study were to determine the home range, habitat use and diet selection of the herd of re-introduced elephants and to document their impact primarily on the key tree species in the reserve. It was found that the home range of these animals was considerably smaller than expected (26 km2) and was strongly associated with the flood plain and tributaries of the only extensive water body on SWR.
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    A hierarchical phytosociology of the Greater Zandvlei area
    (2006) Szöke, Tim; Hoffmann, Timm
    The Zandvlei Nature Reserve is to be expanded to form the Greater Zandvlei Estuary Nature Reserve and will encorporate a much greater area (250 more hectares). The Greater Zandvlei area was classified by means of Zurich Montpellier (Braun Blanquet) procedures. 60 relevés were used to create a hierarchical phytosociology using TWINSPAN and DCA-ordination analyses. 3 major community types were identified, which were then subdivided to reveal 6 community types important to future management: Moist Grassland/Wetland Disturbed Parkland, Dune Asteraceous Fynbos, Thicket/Shrub Mosaic, Rhus-Euclea Dune Thicket and Homogenous Patches. CCA-ordination indicates that the abiotic soil factors sampled (texture composition, pH, carbon content and visible disturbance) explain very little of the variation between the communities (r²=0.002). This phytosociology is provided as a tool for future research in the area, and it is hoped to assist in future management decisions regarding the newly founded GZENR.
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    Historical changes on rocky shores in the Western Cape, as revealed by repeat photography
    (2012) Reimers, Brett; Griffiths, Charles L; Hoffmann, Timm
    Photography has always had a record-keeping purpose, whether to document famous people, or other news-worthy events, such as wars (Webb et al . 2010). Prior to photography becoming a practical tool, researchers in biology relied on drawings and precise descriptions to pass on what they observed during field work (George 1980). In truth, there are very few fields in science which have not made use of photography in some form (George 1980). Taxonomy has been a benefactor, since colour images taken in the field can be used to record distinctive characteristics of organisms that may later lose their pigmentation during preservation (George 1980). Of more relevance to this paper are the many uses of photography in marine ecology which George (1980) suggests are “...to aid site and habitat description, to record the relationship of plants and animals to the environment and to one another, to measure population numbers and the size of individual organisms, and to record the changes in community structure that take place with time.” This list does not take into account the advantages of video to document behavioural studies. As the old adage explains, “a picture is worth a thousand words” and photographs taken at the shore are often far more valuable than lengthy written descriptions used to “set the scene” (George 1980). As with all methods of sampling, however, there is a trade-off between the advantages and disadvantages involved. The disadvantages are similar to those shared with most disciplines interested in sea-shore studies. For example, time is a limiting constraint, as most photographs need to be taken at low tide and indeed the most effective photographic sampling is carried out during spring low tides , when the greatest area of intertidal habitat is exposed. Capturing images during these brief windows often complicates large-scale spatial studies, especially with limited resources (Murray et al . 2006). Furthermore, issues may arise with the detail that can occur due to the resolution of the photograph, as well as identifying taxa of a similar appearance, and problems with analysis may arise where the organisms are in high concentrations and/or stratified (Murray et al . 2006). There are, however, many advantages to the correctly applied photographic method: the greatest perhaps being that the images may be stored and used for further analysis at a later date. These stored images can also be kept on record and used to analyse changes that may have occurred over time. Photographs also have another advantage, in that they are more easily interpreted by people without scientific backgrounds that may not easily understand graphs or complicated figures (Murray et al . 2006). Further examples of the application of photographic techniques in marine biology include photographic surveys and photographic tagging, which has for many years been used in identifying whales, dolphins or seals (McConkey 1999). Photography has also proved useful as a tool for conducting population counts, such as on the West Coast, where seal populations are photographed from the air to determine breeding success (Griffiths et al . 2004). Aerial photography has also been used in conjunction with infra-red photographic techniques to determine the extent of kelp populations along the South African coast (Bolton and Anderson 1990)... This chapter uses repeat photography to illustrate changes that have occurred on rocky shores in the Western Cape over the past hundred years. Changes are documented under four categories; changes in range, climate change, intertidal invasion and direct anthropogenic effects. Images were sourced from books, members of the public and subject specialists and were selected based on their suitability. The sites of the images were identified and repeat photographs captured. The images depict the slow but progressive easterly spread of the kelp Ecklonia maxima and the range contraction of the warmer-water mussel Perna perna. Evidence suggests that a changing climate is the major driver of both of these changes. No change in zonation due to changing sea levels was observed. However, the range contraction of P. perna is complicated by the introduction of an alien mussel, Mytilus galloprovincialis. Repeat photography shows the changes that M. galloprovincialis has caused on the intertidal community in Saldanha Bay. Another invasive organism, Balanus glandula, is shown to have greatly altered the community structure of the Blouberg intertidal zone. Also of interest is the degree of building development that has taken place along the shore. Repeat photography proved a useful tool for documenting changes that are separated by large amounts of time, and is recommended as a useful technique for the surveillance and monitoring of rocky shores.
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    How successful is grassland restoration after removal of pine plantations on the eastern shores of Lake St Lucia?
    (2008) Zaloumis, Nicholas Paul; Bond, William J; Hoffmann, Timm
    The coastal grasslands that occur along the Eastern Shores of Lake St. Lucia are rich in plant species, including endemics. These grasslands in North KwaZulu-Natal, South Africa, are remnants of a severely threatened vegetation type. Large portions of the Eastern Shores have been utilized for commercial pine plantations over the last 50 years; however these have been removed over the last 17 years. It is therefore important that efforts to restore grasslands that have been previously afforested stands of pines are successful. These grassland systems are fire driven and therefore many plants have adapted to these conditions by having massive storage organs below the ground. Using several response variables I was able to assess the effects of plantations on alpha- and beta-diversity and functional traits of forb and other grassland species and attempted to determine whether these disturbed grassland were returning to their original state. A high level of community heterogeneity was found at both scales for natural vegetation, while more homogenous, species low patterns were seen in post-plantation sites. Most notable was the large number of missing resprouting species in pine sites and that, in contrast to forest rehabilitation studies, no evidence for succession was found. The implication of this is massive as grassland rehabilitation may be a lot harder than was previously thought. It is likely that the fire adapted forb species are bad colonizers and have struggled to return to disturbed sites. These grasslands are therefore susceptible to activities that remove or eliminate the considerable amount of below ground biomass from the soil, and these sorts of disturbances should be avoided. Active rehabilitation methods will be required if any progress is going to be made and until such methods are effective considerable effort should be made in conserving the remaining grasslands that we have left and promoting its pharmaceutical, horticultural and societal value.
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    The impacts of indigenous herbivore grazing over five years (2004 - 2008) on vegetation dynamics in four distinct vegetation types of the winter-rainfall Little Karoo
    (2008) Madden, Christine; Hoffmann, Timm
    Vegetation in semi-arid regions is subject to change when heavily utilised by herbivores. Changes in species richness, species and growth form composition, total cover and plant palatability in response to rest (fenced) and grazing (open) treatments was investigated in Sanbona Wildlife Reserve over five years (2004-2008). This reserve is over 55 000 ha and has four dominant vegetation types: Little Karoo Quartz Vygieveld, Western Little Karoo, Montagu Shale Renosterveld and previously transformed Renosterveld classified here as Old Lands. There was no significant change in vegetation dynamics between the fenced or open plots. There were significant differences between years in some vegetation types. All vegetation types showed both treatments having similar shifts in floristic composition. Floristic composition deviated the greatest in 2008 in all vegetation types. This was attributed to an increase in summer and winter rainfall in 2008, as all plots were similarly affected. There was no observed impact of herbivores although disturbance from small rodents and baboons was observed in a few plots. The lack of detectable difference between the fenced and open sites was attributed to low stocking rates, good rainfall and insufficient time.
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    Influence of fire severity in fynbos plant communities and mode of regeneration in the southern Cape Peninsula
    (2011) Retief, Kirsten; Hoffmann, Timm
    Fire severity influences species diversity and alters species habitat requirements, therefore it is important to understand what effect severity has on fynbos communities. The smallest twig diameter of burnt skeletons was used as a severity index and compared between two fire events for 9 permanently marked plots on the southern Cape Peninsula. Species diversity, richness and composition were analysed for one year and eight years after a fire event in 2000 and 3 years after a fire event in 2008. Twig diameters for Erica, Leucadendron, Rhus and Acacia species were significantly greater for the 2008 fire than the 2000 fire event, indicating that the fire was more severe in 2008. The ratio of reseeders to resprouters changed from 8:2 in 2001 and 2008 to 7:3 in 2011 post the second fire event. Thus resprouters were not negatively affected by increased fire severity. Ericoid reseeders appeared to favour more intense fires. Succession of fynbos communities had a greater influence on species diversity, richness and composition than fire severity. Thus fire severity does not influence fynbos communities and factors that influence species survival between fire events, such as succession or alien plant invasions, may be more influential than fire severity.
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    Investigating the impacts of donkeys on a communal range in Namaqualand: how much does a donkey "cost" in goat units?
    (1996) Vetter, Susanne; Bond, William J; Hoffmann, Timm
    Donkeys are used extensively in Namaqualand and other rural areas in South Africa for pulling carts, carrying loads, ploughing and threshing grain. There is, however, an ongoing debate among farmers, agriculturalists and the wider population about the implications of keeping donkeys, particularly on communal lands. Donkeys are reported to cause more damage to the veld than other animals, and it is commonly said that one donkey eats as much as seven goats. This project was initiated as a case study to investigate the impacts of donkeys in a communal area in the succulent shrublands of Namaqualand, and to generate suggestions for the management of donkey populations. The degree of competition between goats and donkeys was investigated by predicting daily food intake using a model based on ruminant and non-ruminant digestion, which takes into account the animal's body weight and digestibility characteristics of its diet. The ratio predicted food intakes is discussed in the light of the degree of dietary and habitat overlap, which were obtained from field observations. Habitat use was scored using dung frequency transects, and feeding was directly observed. It was found that in the wet season, one donkey eats as much as 5 / 7.6 goats (donkey weight set at 200 and 250 kg respectively). In the dry summer, this ratio increases to 7.6 / 8.6 because in ruminants, the passage of food through the gut slows down as the digestibility of the diet decreases. Habitat overlap is concentrated in the riverine areas and sandy pediments, which make up 15 % of the landscape and are strongly favoured by donkeys. No significant differences were found to exist between the intensities of goat use of the different habitats. The botanical composition of the diets of donkeys and goats were found to be similar, but there is a great difference in the quality of the diet consumed by each species as goats are able to select plant parts of a higher quality. The implications of this are that whereas a donkey takes in as much dry matter as 5 - 8.6 goats, the diet of this food is not high enough to satisfy the dietary requirements of goats, and hence fewer goats than predicted can be supported for every donkey that is eliminated. Donkeys are commonly reported to have destructive feeding habits; little of this was directly observed, but donkeys were found to bite deeper into the wood of shrubs, which may damage the plants in the long term. There are two main management measures that should be applied. The feral donkey population in Paulshoek, estimated at 50-100 animals, must be eliminated - even at a conservative estimate, these animals could be replaced with 250 goats. However, one must look beyond the number to the processes taking place to make management effective. Even if one donkey can be replaced with fewer than 5 goats, the vegetation is relieved of the indirect effects donkeys have through their feeding habits. Control of working donkeys should focus on the riverine and flat, sandy areas, as they are potentially of high nutritional importance (especially the riverine areas which support grass throughout the year), and which are also the most susceptible to erosion due to their sparse vegetation cover. These areas are small and valuable, and plans should be made to protect some areas through the growing season.
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    Is the use of Willdenowia incurvata (Restionaceae) for construction at Melkkraal in the Northern Cape sustainable?
    (2004) Watson, Julia; Hoffmann, Timm
    The aim of this study is to evaluate the use of Willdenowia incurvata for the construction of dwellings on a farm outside Nieuwoudtville in the Northern Cape. The research intends to determine how much of the resource (Willdenowia incurvata) is used, the method of utilisation and whether this is environmentally sustainable. An extensive survey of each house in the area was included as a vital part of the study. We did transects to asses the biomass of Willdenowia incurvata in the field; we mapped areas where harvesting takes place; and we performed experimental harvests to determine the typical size and amount of restio used per metre during house construction. On average, it was found that each round house used 2 626kg of restios (wet weight), and rectangular houses used 1 189kg of restios. We found that patch size varied (from 0.19ha to 9.91 ha) and patch biomass varied (from 21 041 hg/ha - 54 021 kg/ha) in the harvested areas. Utilising the general growth rate of Willdenowia incurvata (from Pierce, 1984) and the results of the calculated biomass present in the field and on the houses, three important conclusions were drawn. Firstly, it was found that the amount of restios used as construction material found on the 77 houses in the area is one third less than the amount of restios available in the harvested patches (xkg restios in harvested patches, xkg on houses). Secondly, if harvesting for a few houses (i.e. 10) takes place every five years, it seems that the use of Willdenowia incurvata is sustainable. Therefore no changes to the harvesting method, frequency and intensity are apparently necessary. Thirdly, the harvested areas have a higher density of restios per hectare than the unharvested areas. The use of Willdenowia incurvata for dwelling construction on the farm outside Nieuwoudtville appears to be environmentally sustainable from the findings of this study. It is important to note that this is a snapshot view of the situation, and that assessments of sustainable harvesting practices need to be long term, and continuously reviewed.
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    Land degradation in South Africa
    (2014-09-17) Hoffmann, Timm; Todd, Simon; Ntshona, Zolile; Turner, Stephen
    South Africa has a long history of desertification research which stretches back to the last century. These resources contain literature on water, soil and veld degradation in both commercial and communal areas of South Africa. Also, the most important socio-economic reasons for land degradation are discussed. This resource contains various chapters and factsheets on land degradation in South Africa. A vast amount of data which was generated during the national review of land degradation in South Africa is also available in both GIS and Excel format.
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    Land use and its impact on the Succulent Karoo
    (2004) Jonas, Zuziwe; Hoffmann, Timm; Rouget, Mathieu
    The Succulent Karoo biome (SK biome) is one of the 25 internationally recognized biodiversity hotspots in South Africa with approximately 1940 endemic species. The SK biome is, however, poorly conserved with less than 5% of the area under formal protection. It is also highly threatened by a range of different land use practices. Considering the lack of protected areas and the high levels of endemism (about 40%), which characterize the region, the current and future land use practices are likely to be the key factors in determining the future conservation of the area. Understanding the land use pattern and its drivers that have occurred in the SK biome provides a useful starting point for outlining the future research needs and establishing conservation goals. This project investigates a range of different land use practices such as urban settlement, mining, cropland, conservation and livestock production with their associated environmental drivers. The study used a Geographical Information System (GIS) to map the current extent of land use practices based on available data from different sources in the SK biome. The study also mapped the current extent of livestock density in two land tenure systems (private and communal) of Namaqualand and developed a statistical model to assess the future agricultural potential in the SK biome. The current status of the land use practices in the SK biome shows that most of its area is used for extensive grazing (90%) followed by conservation (4.8%). Due to the aridity of the area, agriculture potential is low. The results confirmed that the conservation status of the SK biome is relatively low but improving, with 4.8% of the biome conserved. Only 3.5%, however, is formally protected in statutory reserves. The remaining conserved area (1.3%) is conserved in non-statutory reserves.
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    Long-term salinity trends in Zandvlei estuary and implications for dominant macroalgae
    (2003) Muhl, Sara; Bolton, John J; Hoffmann, Timm
    Zandvlei is a system that has been highly modified by the urban environment of Cape Town. Salinity is a major driver determining the physical environment of estuaries. The macroalgal community of estuaries forms an important part of the ecology of these systems as primary producers. The salinity of this environment is an important parameter determining the composition, abundance and diversity of these communities. Patterns of salinity fluctuations in the long term (1978-2003) and annually are described in order to establish how communities may vary. Zandvlei is in a Mediterranean climate and salinity was found to vary seasonally and monthly with fluctuations in rainfall. Historical records of macroalgae identified in the estuary were summarized and no record of the Polysiphonia sp., now dominant in the estuary, was found. Dominant macroalgae in the estuary were identified and grown under a range of salinities (0, 1, 5, 10, 20, 29 ppt). Dominant macroalgae included Cladophora sp., Polysiphonia sp. and Enteromorpha prolifera. None of these algae survived at O ppt. In 1 ppt E. prolifera survived but growth was retarded, Polysiphonia sp. survived but did not grow and Cladophora sp. grew successfully at this salinity. All three species have different optimum ranges for growth with E. prolifera preferring higher salinities, Cladophora sp. grew similarly across the range from 1 to 29 ppt and Polysiphonia sp. grew most rapidly at 5 ppt. Depending on the salinity range in the estuary different macroalgae will be dominant. This makes the macroalgae community quite resilient to fluctuating salinities. There should therefore always be estuarine macroalgae present in the estuary provided salinity does not drop below 1 ppt for an extended period. If salinities did drop below 1 ppt there could be an increase in freshwater algae.
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    Long-term vegetation change in the Cape of Good Hope section of Table Mountain National Park, in response to climate, fire and land use
    (2013) Powell, Robyn Faye; Hoffmann, Timm; Gillson, Lindsey
    Climate change, fire and land use are known threats to biodiversity and are predicted to have a major impact on the Cape Floristic Region of South Africa over the next fifty years. This study investigated long-term (1966-2012) changes in the vegetation of the Cape of Good Hope Section of Table Mountain National Park in response to 20th century changes in climate, fire and land use. Climate variables and fire history were assessed over the last 100 years using linear regression, segmented regression and GIS analyses. Seventy eight repeat photographs were taken at stratified points set out across the reserve and changes in total vegetation cover and the cover of major growth forms (broad leaved shrubs, proteoids, ericoids and restioids) within three main vegetation types (Dune Asteraceous Fynbos, Restioid Fynbos and Proteoid Fynbos) were assessed. Transition matrices were used to investigate the extent of vegetation change likely over the next fifty years. In a separate study changes in the number of individuals as well as the cover of several Proteaceae species (Mimetes fimbriifolius, Leucospermum conocarpodendron and Leucadendron spp.) were also investigated using the repeat photographs.